Interlaced scanning and progressive scanning are typical scanning methods employed in a video display device. Interlaced scanning has been employed in current National Television Systems Committee (“NTSC”) television (“TV”) systems. For the video display shown in FIGS. 1A-1C, even and odd fields would be interlaced sequentially and alternately on the screen when displaying a video image. For FIGS. 1A-1C, for interlaced scanning, the solid lines would represent lines being scanned at present, and the dotted lines would represent lines scanned for a preceding display.
Deinterlacing an interlaced signal provides numerous advantages for improving video quality. Specifically, deinterlacing can remove interlace motion artifacts, increase apparent vertical resolution, and reduce flicker. Furthermore, deinterlacing is often required because modern televisions are inherently progressive and the video feed is broadcast in interlaced form.
There are three common techniques for deinterlacing an interlaced video signal. A first deinterlacing technique is known as weaving. Weaving involves combining two adjacent fields into one frame. While this technique maintains vertical resolution, it has the problem of creating interlace motion artifacts if motion is present.
A second deinterlacing technique is known as vertical interpolation. Vertical interpolation involves averaging at least two scan lines to generate a new scan line. The technique is repeated for all scan lines and creates a full frame from a single video field. While vertical interpolation allows a progressive picture to be generated from one video field, half of the resolution of the video feed is lost.
Another deinterlacing technique is known as motion adaptive deinterlacing. For this technique, adjacent fields are merged for still areas of the picture and vertical interpolation is used for areas of movement. To accomplish this, motion, on a sample-by-sample basis, is detected over the entire picture in real time, requiring processing of several fields of a video signal.
To improve the results of the common techniques, a cadence detection algorithm can be implemented. In order for the progressive source to be converted to an interlaced format, each frame from that source must be represented as multiple fields in the interlaced format - i.e., a single frame is converted to 2or more interlaced fields. The conversion process (called telecine) typically results in a regular repeating pattern of fields taken from an original progressive frame. For example, to convert 24 frame/sec film to 60 field/sec interlaced video, a technique known as 3:2 pulldown is used. The technique converts one film frame to 3 fields, the next frame to 2 fields, the next to 3, etc. The result is a regular 3/2/3/2 repeating pattern, or cadence, which can be detected. If the cadence is known, then the original film frame can be reconstructed by simply combining the correct two fields in a weaving operation. However, cadence detection systems are inadequate because they are generally limited to 3:2 pulldown or 2:2 pulldown. Further cadence detection systems incur a number of problems when the cadence pattern is broken for some reason, such as video edits.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.